Wide band omnidirectional beacon antenna



Sept. 11, 1962 J. S. ENGEL ETAL 3,054,107

WIDE BAND OMNIDIRECTIONAL BEACON ANTENNA Filed Aug. 28

RF ENERGY 4 5' 45 IN V EN TORS.

ATTORNEY United States Patent 3,054,107 WIDE BAND OMNIDIRECTIONAL BEACONANTENNA James S. Engel, Tenafly, Howard M. Bellis, Park Ridge, and ErwinJ. Huber, Midland Park, N.J., assignors to International Telephone andTelegraph Corporation,

Nutley, N.J., a corporation of Maryland Filed Aug. 28, 1959, Ser. No.836,779 7 Claims. (Cl. 343761) This invention relates to omnidirectionalbeacon antennas of the type used in producing a multiple-modulationradiation pattern having a fundamental modulation frequency and one ormore additional harmonics of the fundamental modulation frequency foruse in radio navigation systems such as that commonly known as TACANand, more particularly, to means for stabilizing the modulation pattenover a wide range of radio frequencies.

Omnidirectional beacon systems such as TACAN have a high order ofdirectional accuracy which is dependent upon the use of a directiveantenna pattern rotated at a fundamental frequency and modulated by aharmonic of this fundamental frequency so as to produce a generallymultilobed rotating directive radiation pattern. Due to the motion ofthe multiple-modulation antenna pattern, a receiver located remotelyfrom the transmitter receives energy which appears as anamplitude-modulated wave having a fundamental modulation component and amodulation component at a harmonic frequency of the fundamental. Bothfundamental and harmonic frequency reference signals are transmittedomnidirectionally for comparison with the received components of therotating pattern so that the receiver may determine its azimuth relativeto the beacons antenna system.

Basically, the beacon antenna comprises, inter alia, a stationarycentral radiating array around which are rotated at the same angularspeeds two concentric dielectric cylinders. One cylinder carries aconductive parasitic element or elements that produces, in cooperationwith the central radiating array, the fundamental modulation. In asimilar manner, the other cylinder carries a number of parasiticelements or combination of elements corresponding to the harmonic of thefundamental desired to be produced.

In the past, because of the difficulty in stabilizing the modulationpattern over a wide radio frequency spectrum range, the TACAN systemcomprised two bands of operation, viz., low band operation in whichtransmission occurs over a frequency range from approximately 960 to1024 megacycles per second and receives from 1025 to 1087 megacycles,and high band operation in which reception is from 1088 to 1150megacycles and transmission is from 1151 to approximately 1215megacycles. As a result thereof, in the past, two different antennaswere required to cover each of the TACAN bands, each band havirn its owndimensioned fundamental and harmonic parasitic elements as well as itsown dimensioned fundamental and harmonic cylindrical diameters thatdifiered from the corresponding members of the other band. Furthermore,in one type of system, in addition to the dimensional dilferencesmentioned, corresponding parasitic elements of each band were composedof material of different impedance characteristics. While the aboveconsiderations do not limit the usefulness or performance of the TACANsystem, the cost of manufacturing two different antennas, as well as thelack of a standardization between corresponding members of each band,was found to be objectionable.

The principal object of this invention is to provide an omnidirectionalbeacon antenna having a stabilized modulation pattern over a broad radiofrequency bandwidth.

3,354,107. Patented Sept. 11, 1962 Another object is to provide anomnidirectional beacon antenna having uniform and standard parasiticcorresponding elements as well as uniform and standard fundamental andharmonic corresponding cylinders for use in both low and high bandoperation.

A further object of the invention is to provide an omnidirectionalbeacon antenna having an increased bandwidth without substantiallydeviating from the physical dimensions of prior similar antennas.

Still another feature is to provide a single TACAN antenna beaconcovering its entire frequency spectrum range.

According to one aspect of the invention, in an antenna system in whicha group of parasitic conductive elements of a given impedancecharacteristic are disposed for rotation about a central radiator goodmodulation over a wide range of radio frequencies is obtained byincluding a second group of parasitic conductive elements having arelatively different impedance characteristic disposed alternatelybetween the parasitic elements of the first group.

The foregoing and other objects and features of this invention and themanner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof the invention taken in conjunction with the accompanying drawingscomprising FIGS. 1 to 4 wherein:

FIG. 1 is a view in perspective of the preferred embodiment of theomnidirectional beacon system of this invention;

FIG. 2 is a sectional view of the embodiment of the antenna system takenalong the lines 22 of FIG. 1; 7

FIG. 3 is a view of one of the groups of parasites of the preferredembodiment for harmonic modulation, and one of the groups of parasitesfor stabilizing the depth of modulation; and v i 7 FIG. 4 is a partialperspective view of another embodiment of the omnidirectional beaconsystem of this invention.

In the preferred embodiment of the invention, the parasitic elements aredisposed above a counterpoise, and the radiator is a monopole disposedcentrally over the counterpoise. Further, in the preferred embodimentthe parasitic elements are placed on dielectric cylinders, with onegroup of parasites on an inner cylinder for fundamental modulation and aplurality of groups of parasites on an outer cylinder for harmonicmodulation.

Referring to FIGS. 1 and 2 of the drawing, an antenna system forproducing a rotating multilobed shaped azimuth directivity patterncomprises a central radiator 1 supported at the center of a counterpoise2. A harmonic frequency series of parasites composed of V- shaped groupsof conductive parasitic elements 3, 3a spaced at regular angularintervals are affixed to the surface of an outer rotating fiberglasshousing'4 while a fundamental frequency group of parasitic elements '5is attached to an inner fiberglass housing 6.

Referring more specifically to FIG. 2 of the drawing, a variable source23 of radio-frequency (-R-F) energy is coupled to a coaxial transmissionline 7. The inner conductor is coupled to a central radiator 1 whichessentially comprises a quarter wavelength vertical stub antenna. Acounterpoise 2 which includes an inner stationary disk 8 and an outerrotating disk 9 surrounds the central radiator assembly. The outerconductor of transmission line 7 is coupled to disk 8. A quarterwavelength choke generally indicated at 10 is provided by overlappingdisks 8 and 9 so that there is no leakage of energy as the meta-1 disk 9rotates. The outer edge of disk 9 has a flange 1-1 which acts as aradio-frequency choke to prevent undesired radiation. Surrounding thecentral radiator assembly 1 is an inner fiberglass housing 6,

tal flange 13 attached to disk 9.

. acteristic.

. 3 which includes a generally horizontal portion 12 which extends overthe outer edge of disk 8 and is attached to disk 9, as for example, bymeans of mounting screws 15 located in equidistant slots 16 on flange20. The fundamental frequency parasitic group of elements is carried bythe inner fiberglass housing 6 which rotates about the central radiator-1. Also rotating with the metal disk counterpoise 2 is an outerfiberglass housing 4 on which a plurality of parasitic element groups 3,3a are carried for the harmonic modulation. Housing 4 has a horizon- Themetal disk 9 and the attached housings 4 and 6 are rotated by means of a'motor 14.

radiator at which the desired radiation component of each is near amaximum, as determined by the Bessel Function expansion; and each isdesigned in length, resistance, and position to produce the desiredradiation char- Further information on TACAN may be found in ElectricalCommunications, published by In- .ternational Telephone and TelegraphCorporation, New ,York, N.Y., volume 33, No. 1, March 1956, with theprinciples of antena design on pages 35 to 59.

In the embodiment shown here, the parasites and counterpoise disk 9 arerotated at 15 cycles per second, which ..is the fundamental modulationfrequency produced by .the single group of parasites 5 on housing 6.parasites 3, 3a produce the ninth harmonic of modula- The tion at 135cycles per second, and there are nine groups .of these parasites 3, 3aspaced at 40 intervals on housing 4.

It has been found that with the harmonic parasites 3,

3a adjusted to produce maximum modulation at some predeterminedoperating radio frequency, that the depth of modulation decreases forthe lower frequencies and increases for the higher frequencies.According to the invention, in order to stabilize the depth ofmodulation over a substantial range of operating frequencies, a

, second series of modulation controlling parasites with a relativelydifferent impedance characteristic from the former series is disposedfor rotation about the central radiator 1. The effect is that the firstseries continues to provide the majority of the modulation while thesecond series reduces the modulation at the upper frequencies andincreases the modulation at the lower frequencies.

In the embodiment shown in FIG. 1, the parasitic elements 17 and 17acomprise a group of the second series. The number of groups of thesecond series corresponds to the harmonic selected, which in this casewould be nine. For the sake of simplicity, the groups 17, 17a of thesecond series are mounted on the same fiberglass housing 4 as the firstseries, it being obvious, however,

that they may be mounted on their own housing as long i as they rotateat the same angular speed as their associated group in the first series.

Referring to FIG. 3, the harmonic modulation group of the first seriescomprises the two elements 3, 3a that are symmetrically disposed about acenter line 18 and slant upward and away from the center line 18 atequal angles therewith. As explained in the copending United StatesPatent Application Serial No. 672,543, of C. Lucanera and H. Avery,entitled Omnidirectional Beacon Antena filed July 15, 1957, now PatentNo. 2,912,693, the purpose of the V-shaped elements 3, 3a

is to provide sufiicient modulation up to high vertical angles. Themodulation controlling group of the second series, as shown in FIG. 3,comprises the slanted inverted V-shaped elements 17, 17a that aresymmetrically disposed about the center line .18 of the group of thefirst series and form equal angles therewith with the elements 17, 17aslanting downward and away from center line 18.

When the changes in modulation are negligible for changes in verticalangle, an arrangement of vertical parasites may be employed asillustrated in FIG. 4 in which the corresponding parts of FIG. 1 aregenerally indicated by like reference numerals. The vertical parasites3b provide the majority of modulation while the other parasites 17bcontrol the modulation for changes in radio frequency as explained aboveby having relatively ditferent impedance characteristics. In theembodiment shown in FIG. 4 the vertical parasites 3b are symmetricallyspaced 40 from each other about the fiberglass housing .4. Thecontrolling modulation parasites 17b are also spaced symmetrically aboutthe fiberglass housing 4 with each parasite 17b placed midway betweentwo consecutive parasites 3b.

While specific configuration and combination of the groups of the firstor second series of the embodiment are shown in FIGS. 1 and 4, it isunderstood that there are other possible configuration and combinationsthat will produce the desired effects, as for example, the invertedV-shaped groups 17, 17a of the second series in FIG. 1 may be combinedwith the vertical parasite 3b in FIG. 4. Furthermore, it is obvious thatthe modulation control over a substantial frequency range may beeifected even on a fundamental frequency group, as for example, thefundamental frequency group of parasitic elements 5, in a similar manneras was done for the harmonic groups 3, 3a or 3b.

In order to provide correct bearing information, it is important thatthe fundamental and harmonic modulation waves be maintained at apredetermined phase relationship with each other. It has been found thatwith the antenna designed to maintain the desired phase relationshipover a maximum bandwidth of operating frequencies, that a phase reversaloccurs when the antenna operates outside this bandwidth. According tothe invention, in order to maintain the desired phase relationship,means are included to orient relatively the fundamental parasites withrespect to the harmonic parasites. One such means includes, a pair ofpositioning holes 19, spaced 180 apart which are provided on the flange20 of the fundamental fiberglass housing 6 at an optimum position forproducing the desired phase relationship. A corresponding pair ofmatched positioning holes 21 are similarly located on the rotatable disc9. The fundamental housing 6, by means of the positioning pins 22 andscrews 15, is thus oriented with the harmonic housing 4 at the desiredphase relationship. When a phase reversal occurs, the housing 6 isshifted 180 to maintain the phase relationship. In a similar manner, toprovide for phase shifts of other than "180 a plurality of positioningholes, not shown, may be located about the periphery of the flange 20*at regular or other desired spaced intervals.

For the radio frequency range of 960 to 1215 megacycles, the harmonicparasite groups 3, 3a may be on a housing 4, thirty-seven inches indiameter. The V- shaped elements 3 and 3a may each be four inches longand the inverted V-shaped elements 17 and 17a may each be seven incheslong. The elements 3 and 3a of the harmonic group may be at an angle of90 to each other, and the elements 17 and 17a of the modulation controlgroups may also be at an angle of 90 to each other. The parasiticelements 3 and 3a may be made of a resistance wire having a resistivityof 700 ohms per foot, depending upon the amount of modulation desired.The parasitic elements 17 and 17a may be made of wire having aresistivity of approximately 400 ohms per foot depending on the amountof control desired. With these values an impedance ratio of about 2:1 isestablished between the parasitic elements 3, 3a and the parasiticelements 17, 17a. An antenna having the dimensions and characteristicsgiven above will produce harmonic modulation over the range which iswithin the acceptable limits of 12 to 30 percent at vertical angles fromzero to 50 or more. With this diameter, transmission occurs from 960 to1025 megacycles and is achieved without phase shift. For the highertransmission frequencies,

viz., 1150 to 1215 megacycles; a reversal of the fundamental modulationparasite is required as explained above.

While we have described above the principles of our invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of our invention as set forth in the objects thereof and inthe accompanying claims.

We claim:

1. An antenna system of a predetermined continuous range of frequenciescomprising a vertically disposed elongated radiator, a variable sourceof radio frequency energy coupled to said radiator .and including saidrange, a first dielectric rotatable cylinder disposed concentricallyabout said radiator, at least one conductive parasite carried by saidfirst cylinder to produce a fundamental modulation of said radiofrequency energy, a second dielectric rotatable cylinder disposedconcentrically about said radiator, a predetermined number of firstgroups of conductive parasites having predetermined impedancecharacteristics carried by said second cylinder to superimpose aharmonic modulation of said fundamental modulated radio frequencyenergy, said harmonic corresponding to said predetermined number, a saidpredetermined number of second groups of conductive parasites havingrelatively difierent impedance characteristics from said first group andcarried by said second cylinder in a predetermined spatial relationshipto said first groups to stabilize the depth of modulation of said radiofrequency energy over the said range, said range further includingtherein .at least one band of frequencies at which said harmonic andfundamental modulation will undergo a phase shift from somepredetermined phase relationship established between said fundamentaland harmonic, means to orient relatively said group of conductiveparasites on said first cylinder with respect to said first and secondgroups of conductive parasites on said second cylinder to maintain saidpredetermined phase relationship.

2. An antenna system of a predetermined continuous range of frequenciescomprising .a vertically disposed elongated radiator, a variable sourceof radio frequency energy coupled to said radiator and including saidrange, a first dielectric rotatable cylinder having a firstpredetermined diameter disposed concentrically about said radiator,parasites carried by said first cylinder to produce a fundamentalmodulation of said radio frequency energy, a second dielectric rotatablecylinder having a second predetermined diameter relatively differentfrom said first predetermined diameter, a predetermined number of firstgroups of conductive parasites having predetermined impedancecharacteristics carried by said second cylinder to superimpose aharmonic modulation of said fundamental modulated radio frequencyenergy, said harmonic corresponding to said predetermined number, a saidpredetermined number of second groups of conductive parasites having arelatively different impedance characteristic from said first group andcarried by said second cylinder in predetermined spatial relationship tosaid first groups to stabilize the depth of modulation of said radiofrequency energy over said range, a rotatable member connecting saidfirst .and second cylinders including first coupling means to maintainsaid first and second cylinders in a first predetermined relationship,said range further including therein at least one band of frequencies atwhich said harmonic and fundamental modulation will undergo a phaseshift from some predetermined phase relationship established betweensaid fundamental and harmonic, means to orient relatively said parasiteson said first cylinder with said groups of conductive parasites on saidsecond cylinder to maintain said predetermined phase relationship whensaid antenna operates within said band, said latter means including saidrotatable member having a second coupling means to maintain said first 6and second cylinder in a second predetermined relationship to maintainsaid phase relationship.

3. An antenna system of .a predetermined continuous range of frequenciescomprising a vertically disposed elongated radiator, a variable sourceof radio frequency energy coupled to said radiator and includingsaid'range, a first dielectric rotatable cylinder having a firstpredetermined diameter disposed concentrically about said radiator,parasites carried by said first cylinder to produce a fundamentalmodulation of said radio frequency energy, a second dielectric rotatablecylinder having a second predetermined diameter relatively dii ferentfrom said first predetermined diameter, a predetermined number of firstgroups of conductive parasites having predetermined impedancecharacteristics carried-by said second cylinder to superimpose aharmonic modulation of said fundamental modulated radio frequencyenergy, said harmonic corresponding to said predetermined number, a saidpredetermined number of second groups of conductive parasites having arelatively different impedance characteristic from said first group andcarried by said second cylinder in predetermined spatial relationship tosaid first groups to stabilize the depth of modulation of said radiofrequency energy over said range, a rotatable member connecting saidfirst and second cylinders including first coupling means to maintainsaid first and second cylinders in .a first predetermined relationship,said range further including therein at least one band of frequencies atwhich said harmonic and fundamental modulation will undergo a phaseshift from some predetermined phase relationship established betweensaid fundamental and harmonic, means to orient relatively said parasiteson said first cylinder with said groups of conductive parasites on saidsecond cylinder to maintain said predetermined phase relationship whensaid antenna operates Within said band, said latter means including saidrotatable member having a second coupling means to maintain said firstand second cylinder in a second predetermined relationship to maintainsaid phase relationship, each of said first groups further comprising apair of parasitic elements symmetrically disposed about a verticalcenter line of the said pair at an angle of 45 thereto, said elements ofsaid first group being closest together at their lowest point andslanting away from each other and the said center line at their highestpoint, and each of said second groups further comprising a pair ofparasitic elements symmetrically disposed about the said vertical centerline at an angle of 45 thereto, each of said elements of said secondgroup being closest together at their highest point and slanting awayfrom each other and the said center line at their lowest point the saidelements of said second group being further disposed about the saidelements of said first group.

4. An antenna system of a predetermined continuous range of frequenciescomprising a vertically disposed elongated radiator, a variable sourceof radio frequency energy coupled to said radiator and including saidrange, a dielectric rotatable cylinder disposed concentrically aboutsaid radiator, a first plurality of groups of conductive parasitescarried by said cylinder to modulate said radio frequency energy, eachgroup of said first plurality of groups including a pair of conductiveparasites having a predetermined impedance characteristic, and means tostabilize the depth of said modulation over said range including asecond plurality of groups of conductive parasites carried by saidcylinder in a predetermined spatial relationship to the groups of saidfirst plurality of groups, each group of said second plurality of groupsincluding a pair of conductive parasites having an impedancecharacteristic different than said predetermined impedancecharacteristic.

5. An antenna system of a predetermined continuous range of frequenciescomprising a vertically disposed elongated radiator, a variable sourceof radio frequency energy coupled to said radiator and including saidrange,

a dielectric rotatable cylinder disposed concentrically about saidradiator, at least a first pair of conductive parasites carried by saidcylinder to modulate said radio vfirequency energy, each conductiveparasite of said first pair of conductive parasites having apredetermined impedance characteristic, and means to stabilize the depthof said modulation over said range including at least a second pair ofconductive parasites carried by said cylinder in a predetermined spatialrelationship to said first pair of conductive parasites, the conductiveparasites of said second pair of conductive parasites having animpedance characteristic different than said predetermined impedancecharacteristic.

6. An antenna system of a predetermined continuous range of frequenciescomprising a vertically disposed elongated radiator, a variable sourceof radio frequency energy coupled to said radiator and including saidrange, a dielectric rotatable cylinder disposed concentrically aboutsaid radiator, a first plurality of groups of conductive parasitescarried by said cylinder to modulate said radio frequency energy, eachgroup of said first groups of conductive parasites including a pair ofconductive para- ,sites having a predetermined impedance characteristic,

and means to stabilize the depth of said modulation over said rangeincluding a second plurality of groups of conductive parasites carriedby said cylinder, the groups of said second plurality of groups beingdisposed in an alternate relationship with the groups of said firstplurality energy, each parasite of said first pair having apredetermined impedance characteristic and being disposed symmetricallyon opposite sides of a vertical center line with the parasites of saidfirst pair being closest together at their lowest point and slantingaway from each other and said center line to form equal anglestherewith, and means to stabilize the depth of said modulation over saidrange including at least a second pair of conductive parasites carriedby said cylinder, each parasite of said second pair having an impedancecharacteristic different than said predterrnined impedancecharacteristic and being disposed symmetrically on opposite sides ofsaid center line with the parasites of said second pair being closesttogether at their highest point and slanting away from each other andsaid center line toform equal angles therewith.

References (lited in the file of this patent UNITED STATES PATENTSLucanera et al. Nov. 10, 1959

